Production of cutinolytic esterase by filamentous bacteria

Thirty-eight strains of filamentous bacteria, many of which are thermophilic or thermotolerant and commonly found in composts and mouldy fodders, were examined for their ability to produce cutinolytic esterase (cutinase) in culture media supplemented with cutin, suberin or cutin-containing agricultural by-products. Initially, the ability of culture supernatants to hydrolyse the artificial substrate p-nitrophenyl butyrate was determined by spectrophotometric assays. Only one bacterium, Thermoactinomyces vulgaris NRRL B-16117, exhibited cutinolytic esterase production. The enzyme was highly inducible, was repressed by the presence of glucose in the medium and hydrolysed both apple and tomato cutins. Inducers included apple cutin, apple pomace, tomato peel, potato suberin and commercial cork. Unlike similar fungal enzymes, the T. vulgaris cutinolytic esterase was not inducible by cutin hydrolysate. The cutinolytic esterase exhibited a half-life of over 60 min at 70 °C and a pH optimum of ≥ 11·0. This study indicates that thermophylic filamentous bacteria may be excellent commercial sources of heat-stable cutin-degrading enzymes that can be produced by fermentation of low cost feedstocks.